1. Field of the Invention
This invention relates to a method for minimizing iron contamination of reforming or hydroforming catalysts during catalyst regeneration.
2. Description of Related Art
Regeneration and reactivation of noble-metal containing catalysts typically requires one or more cycles of a sequence of steps which include (i) oxidation of the catalyst in an oxidizing atmosphere in a controlled burn off of the carbon from the coked catalyst, (ii) reduction of the oxidized metallic components of the catalysts in a hydrogen atmosphere, and (iii) treatment of the catalyst by contact of same with halogen, an admixture of halogen and oxygen, or an admixture of halogen, halide and oxygen, to redisperse the agglomerated noble metal component, e.g., iridium-containing metallic components. Regeneration and reactivation of the catalyst results in the formation of a large amount of iron scale within the regeneration circuit of the reactor system. When the iron scale is carried into the catalyst bed by the flow stream the iron scale reacts with the catalyst during catalyst regeneration and suppresses the activity of the freshly regenerated catalyst. The migration of scale from the regeneration circuit to the beds of catalyst within the reactor is particularly troublesome at the location in the bed first contacted by the gases from the regeneration circuit, e.g., at the top of the beds in a downflow reactor. Catalyst activity depression at this location can thus be particularly severe when iron is chemically bound to the surface of the catalyst.
Exclusion of the iron scale from contact with the catalyst has been achieved to some extent by a number of prior art techniques. These include dumping the catalyst from the reactor and/or screening off the most contaminated portion of the catalyst in the reactor. However these techniques still leave very fine iron particles adhering to the catalyst or catalyst extrudate surfaces. The installation of an on-stream filter in advance of the reactor has also been tried, but this has resulted in significant capital expenditures, as well as increased production costs due to the pressure drop within the regeneration circuit. Attempts to remove very fine particles using a fine mesh filter also results in an unacceptable pressure drop through the reactor.
However the earlier references do not specifically address how to prevent iron contamination that would render catalyst regeneration less effective. In fact, the relatively high temperatures of greater than 500.degree. C. employed in the hydrogen reduction steps of the regeneration processes disclosed in these patents will also reduce most of the iron scale present in the system to the metallic form of iron, which then makes physical contact with the catalyst particles. This form of iron is in turn reactive with the hydrogen chloride employed later in the process, resulting in the generation of ferrous chloride (FeCl.sub.2) which, although non-volatile, has a surface mobility which allows it to move into catalyst particles and contaminate the catalyst